In recent years, scanner systems have been widely employed in the field of photomechanical process. Light sources of the scaner include a glow lamp, a xenon lamp, a tungsten lamp, an LED, an He-Ne laser, an argon laser, and a semi-conductor laser. Among the scanner systems, a dot generator system which directly forms a dot image through electrical signals has been spreading, and an argon laser has conventinally been used as a light source for the scanner of the dot generator system because of its high output, Since an argon laser, however, makes the recording apparatus bulky and expensive, scanners using an He-Ne laser (wavelength: 632.8 nm) as a light source which are more compact and cheaper have recently been developed.
On the other hand, since an LED (wavelength: 660 to 680 nm) is more small-sized and lightweight as compared with other light sources, light-emitting elements thereof can be integrated so that a plurality of lines may be scanned at once to thereby achieve speeding up of the process. Besides, since the light-emitting elements of the LED are solid and can therefore be directly modulated, they are lighted only at the time of recording. Accordingly, the elements have a long life and are of low cost as compared with semi-conductor lasers, etc. From these reasons, scanners using an LED light source are also undergoing developments.
Light-sensitive materials for use in these scanners are required to satisfy various characteristics. That is, they are required to have high spectral sensitivity to the wavelength of the respective light source and to exhibit high sensitivity and high contrast even when exposed at a high intensity of illumination for a short time of from 10.sup.-3 to 10.sup.-7 sec. In the field of facsimile, the light-sensitive materials are required to have resistance to high-temperature and high-speed processing from the standpoint of preferential demand for rapid response and also safety against a bright green safelight from the standpoint of working efficiency.
In order that high sensitivity and high contrast may be assured in the high-intensity and high-speed exposure (10.sup.-3 to 10.sup.-7 sec) using an He-Ne laser or an LED as a light source, the sensitivity of a silver halide emulsion or the spectral sensitivity of a spectrally sensitized silver halide emulsion should be high on the high-intensity and high-speed exposure. For this purpose, a method for increasing sensitivity of an emulsion by introducing an iridium salt to silver halide is frequently adopted as disclosed in JP-A-48-60918, 58-211753, 61-29837 and 61-201233 ( the term "JP-A" as used herein means an "unexaminee published Japanese patent application) and JP-B-48-42172 (the term "JP-B" as used herein means an "examined published Japanese patent application"). Spectral sensitizing dyes for general purpose of obtaining a red-sensitive emulsion are described in JP-B-43-4933, 48-42172 and 55-39818 and JP-A-50-62425 and 54-18726.
It has been turned out that such a highly sensitive emulsion exhibits high sensitivity and high contrast on actual exposure, but, in turn, frequently shows an increased sensitivity at a low intensity of illumination, resulting in significant reduction of safety from the above-described bright green safelight.
In order to solve this problem, dyes absorbing light in a specific wavelength region are frequently used for coloring a photographic emulsion layer or other layers. Because the layer to be colored, in many cases, comprises a hydrophilic colloid, a water-soluble dye is generally incorporated in the layer. Such a dye should satisfy the following conditions:
1) The dye should have a proper spectral absorption according to the end use. PA0 2) The dye should be photochemically inactive. Namely, it should not give any adverse influences, in a chemical sense, to a silver halide photographic emulsion layer, such as reduction in sensitivity, regression of the latent image, and fog. PA0 3) The dye should be discolored or removed by dissolution during photographic processing, thus leaving no harmful color in the processed photographic material.
Much efforts have been made in the art to discover a dye meeting these requirements.
Of various dyes so far developed, oxonol dyes having two pyrazolone nuclei are discolored in a developer containing a sulfite and have been used as dyes giving reduced adverse influences to a photographic emulsion. For example, oxonol dyes having a sulfoaryl group at the 1-position of the pyrazolone nucleus are described in JP-B-39-22069, 51-46607, 55-10061, 60-53304, and 51-1419; and those having a sulfoalkyl group at the 1-position of the pyrazolone nucleus are described in JP-A-49-99620 and 55-10059. Although the dyes of these types do not seriously affect a photographic emulsion per se, they have been proved disadvantageous for an emulsion having been spectrally sensitized. Namely, they cause spectral sensitization in an undesired region or reduction in sensitivity which is assumably attributed to desorption of a sensitizing dye.
In addition, some of these dyes remain in the photographic material after processing depending on the type of rapid processing which is currently employed. In order to overcome the problem of color remaining, it has been proposed to use a dye highly reactive with a sulfite ion. Such a dye, however, causes reduction of density with time due to insufficient stability in photographic layers, failing to attain desired photographic effects.
On the other hand, dyes having a sulfoaralkyl group at the 1-position of the pyrazolone nucleus and a specific substituent at the 3-position of the pyrazolone nucleus as disclosed in JP-A-50-145125, 50-147712, and 52-20830 are not sufficiently discolored, causing color remaining.